Method for discharging reduced product from a moveable-hearth furnace and a discharging device

ABSTRACT

A method for discharging a reduced product produced on a movable hearth of a movable-hearth furnace uses a discharging device. The discharging device includes a removal unit for removing the reduced product from the movable hearth, a separation unit for separating the reduced product from a solid reductant, a leaving-returning unit for either leaving substances other than the reduced product on a solid reductant layer or returning the substances onto the solid reductant layer, and a discharge unit for discharging the reduced product to the outside of the movable-hearth furnace.

BACKGROUND

[0001] 1. Field of the Invention

[0002] This invention relates to a technology for discharging productsfrom a movable-hearth furnace. In particular, this invention relates toa technology for discharging a reduced product to the outside from amovable-hearth furnace and a discharging device of the reduced product,the reduced product being obtainable such that raw materials includingmetallic ingredients such as ores containing minerals and dust andsludge produced in ironworks and industrial wastes are accumulated on amovable hearth together with a solid reductant, and the accumulated rawmaterials are reduced. Particularly, the invention relates to atechnology for selecting a reduced product having a large grain size anddischarging the reduced product, and a device for separating the reducedproduct from a reductant to be left in a furnace.

[0003] 2. Description of the Related Art

[0004] Steel, which is a typical reduced metal, is generally produced ina converter or an electric furnace. For example, scrap and reduced ironare melted with heat by using electric energy, and are smelted, asneeded, thereby forming steel in an electric furnace. Recently, however,the supply of and demand for scrap are tight, and high-quality steel issought on an increasing basis. Therefore, there is a tendency to usereduced iron.

[0005] A so-called “movable-hearth-furnace” method which is a processfor manufacturing reduced iron and the like is disclosed in, forexample, Japanese Unexamined Patent Application Publication No.63-108188, in which an iron ore and a solid reductant are charged anddeposited on a hearth movable in a horizontal direction, and the ironore is heated and reduced by radiation heat transfer by a burner fromabove the hearth, thereby manufacturing the reduced iron. In amovable-hearth furnace used in this method, the raw material is chargedand heated while the hearth is horizontally moved in a heating zone,generally, in a circle (revolving). In other words, a rotary hearthfurnace is used.

[0006] In the rotary hearth furnace, pellets including an iron ore and asolid reductant are charged and heated on the hearth, thereby reducingthe iron ore and producing reduced pellets. The hearth of the furnacemoves in a heated furnace. Therefore, a heat-resistive material isapplied on a surface of the hearth, or, sometimes, heat-resistive grainsare deposited on the heat-resistive material applied on the surface,thereby protecting the surface of the hearth.

[0007] A rotary-hearth furnace as a movable-hearth furnace is disclosedin, for example, Japanese Unexamined Patent Application Publication No.11-172312. In FIG. 1, the rotary-hearth furnace includes an annularfurnace 10 provided with a pre-heating zone 10 a, a reducing zone 10 b,a melting zone 10 c, and a cooling zone 10 d, and an annular movablehearth 11 is disposed in the furnace 10. A mixture 12 of a raw materialsuch as an iron ore and a solid reductant such as coal, coal char andcoke is charged and deposited on the movable hearth 11. A heat-resistivematerial is applied to the surface of the movable hearth 11 of thefurnace 10. However, the movable hearth 11 may be protected with a layerof a solid reductant which is formed between the movable hearth 11 andthe mixture 12.

[0008] Burners 13 are disposed in an upper part of the furnace 10. Anoxidized material including metals, such as iron ore, deposited on themovable hearth 11 is heated and reduced by using heat of combustion ofthe burners 13, thereby forming a reduced material such as reduced iron,and the reduced material is further heated to be melted, thereby forminga reduced product including metals with slag. A charging device 14 forcharging a raw material onto the movable hearth 11 and a dischargingdevice 15 for discharging a reduced product are shown in FIG. 1. In thetechnology disclosed in Japanese Unexamined Patent ApplicationPublication No. 11-172312, a bed of a solid reductant having a giventhickness is formed by depositing the powdered solid reductant on ahearth, a bed of a metal-containing material having a given thickness isformed by depositing the powdered metal-containing material on thesurface of the bed of the solid reductant, and a plurality ofconcavities are formed in the bed of the metal-containing material fromthe surface thereof to the surface of the bed of the solid reductant.The metal-containing material heated at the surface thereof is reducedand melted, and gathers in the concavities remaining in the bed of thesolid reductant by the effect of surface tensity and gravity of themelted material while being divided into a metal and slag. A pluralityof large grains of the metal with slag are obtained in the concavitiesby cooling the melted material.

[0009] The reduced product and the like produced on the movable hearth11 are generally discharged by using the discharging device 15 from themovable hearth 11 to the outside of the furnace. A screw-feeder-typedischarging device as a device for discharging the reduced product andthe like from a hearth is disclosed in, for example, Japanese UnexaminedPatent Application Publication No. 11-172312. The screw-feeder-typedischarging device disclosed therein includes a rod 15 a provided with aspiral screw 15 b fixed around the rod 15 a, as shown in FIG. 2. The rod15 a of the screw-feeder-type discharging device is disposedsubstantially perpendicular to the direction of movement of the movablehearth 11 and rotates on the movable hearth 11, whereby the reducedproduct 16 including reduced pellets and a metal disposed on the hearth11 is collected in a direction substantially perpendicular to thedirection of movement of the hearth 11 and is discharged from the hearth11.

[0010] The technology is characterized in that the reduced product 16which is, for example, reduced iron as a metal not including a gangueportion can be substantially completely discharged in a transversaldirection of the hearth 11 by driving the screw 15 b of thescrew-feeder-type discharging device while the screw 15 b issubstantially in contact with the upper surface of the hearth 11.

[0011] Grains of a metal with slag as a reduced product and the solidreductant can be substantially completely discharged by using the abovescrew-feeder-type discharging device shown in FIG. 2 in thesolid-reductant-bed-type reducing-melting process. The discharged grainsof the reduced product 16 and the solid reductant are classified by ascreen. The grains of a metal with slag are classified as manufacturedgoods and the solid reductant which falls through the screen is reusedin the furnace.

[0012] In this technology, a mixed raw material which is a mixture ofpowdered iron ore and a solid reductant is deposited in a layer on asolid reductant layer 1 b disposed on a hearth 11, is reduced at a giventemperature, and is heated to be melted and divided into metals andslag, whereby reduced iron not including a gangue portion is produced.

[0013] However, when the screw-feeder-type discharging device describedabove, which collects the produced reduced iron with a screw of thescrew-feeder-type discharging device, discharges a pellet-shaped reducedproduct in particular, there is a risk that the driving device stopswhen the pellet-shaped reduce product is “bitten” or becomes wedgedbetween the screw and the hearth, which fact acts as a pressing forceapplied to the hearth, thereby damaging the surface of the hearth.

[0014] By the discharging method described above, deposited substanceson the movable hearth are completely discharged to the outside. However,there is a drawback in that the reduced product 16 (metals) cannot beseparated from the solid reductant so as to be collected (discharged) asa manufactured good, although the substances including metals and slagdeposited on the movable hearth can be completely discharged by theknown technology.

[0015] Another drawback has been found in the known discharging methodin that the temperature of the solid reductant is significantly reducedduring classification, thereby generating thermal loss, in which thereduced product 16 and the solid reductant 65 are completely dischargedto the outside for classification and the solid reductant is rechargedinto the furnace. The solid reductant is preferably returned into thefurnace while it is hot, thereby avoiding thermal loss.

OBJECTS OF THE INVENTION

[0016] Accordingly, it is an object of the invention to provide adischarging device and a discharging method using the discharging devicein which damage to the hearth of a movable-hearth furnace can beavoided.

[0017] It is another object of the invention to provide a dischargingdevice and a discharging method using the discharging device in which areduced product such as reduced iron can be selectively discharged froma hearth of a movable-hearth furnace, and a solid reductant can be lefton the hearth of the movable-hearth furnace, whereby thermal loss can beavoided.

SUMMARY OF THE INVENTION

[0018] To these ends, according to an aspect of the invention, a methodfor discharging a reduced product produced on a movable hearth of amovable-hearth furnace comprises the steps of removing the reducedproduct from the movable hearth; separating the reduced product from asolid reductant; either leaving substances other than the reducedproduct on a solid reductant layer or returning the substances onto thesolid reductant layer; and discharging the reduced product to theoutside of the movable-hearth furnace.

[0019] In the method described above, the step of removing the reducedproduct from the movable hearth may comprise the step of attracting thereduced product by using a magnetic force to remove the reduced productfrom the movable hearth.

[0020] The method for discharging a reduced product produced on amovable hearth of a movable-hearth furnace, according to the invention,may further comprise the step of cooling the reduced product beforeattracting the reduced product by using a magnetic force to remove thereduced product from the movable hearth.

[0021] The step of removing the reduced product from the movable hearthmay comprise the step of scooping the reduced product and the solidreductant by using a screen, and the step of separating the reducedproduct from the solid reductant may comprise the step of sifting thereduced product and the solid reductant according to the grain size ofthe reduced product and the solid reductant by using the screen.

[0022] The step of sifting the reduced product and the solid reductantaccording to the grain size of the reduced product and the solidreductant by using the screen, whereby the reduced product and the solidreductant having smaller grain sizes are left on the movable hearth, maycomprise the step of selecting the reduced product having a larger grainsize by using a rotary drum which spans the movable hearth of themovable-hearth furnace in the widthwise direction of the movable hearthand is provided with a plurality of net-shaped or comb-shaped screenseach extending in a radial direction of the rotary drum from theperiphery thereof.

[0023] The step of sifting the reduced product and the solid reductantaccording to the grain size of the reduced product and the solidreductant by using the screen, whereby the reduced product and the solidreductant having smaller grain sizes are left on the movable hearth, maycomprise the step of removing the reduced product having a larger grainsize from the solid reductant layer and discharging the reduced productby using a screw feeder which spans the movable hearth in the widthwisedirection of the movable hearth and extends to the outside of themovable-hearth furnace, and which operates in such a manner that a partof the solid reductant is left on the solid reductant layer bycontrolling the position of the axis of the screw feeder with respect tothe movable hearth. A plurality of apertures may be formed in a casingof the screw feeder, the apertures being arrayed along the axis of thescrew feeder, and the reduced product and the solid reductant havingsmaller grain sizes may be left on the solid reductant layer by usingthe casing of the screw feeder. The casing provided with the pluralityof apertures may be a cylindrical screen which covers the screw feeder.The method described above may further comprise the steps of classifyingthe reduced product and the solid reductant according to the grain size;and returning the reduced product and the solid reductant having smallergrain sizes either onto the solid reductant layer formed on the movablehearth of the movable-hearth furnace or to a layer of mixed rawmaterials formed on the solid reductant layer.

[0024] According to another aspect of the invention, a dischargingdevice for discharging a reduced product produced on a movable hearth ofa movable-hearth furnace comprises a removal unit for removing thereduced product from the movable hearth; a separation unit forseparating the reduced product from a solid reductant; aleaving-returning unit for either leaving substances other than thereduced product on a solid reductant layer or returning the substancesonto the solid reductant layer; and a discharge unit for discharging thereduced product to the outside of the movable-hearth furnace.

[0025] In the discharging device described above, the removal unit forremoving the reduced product from the movable hearth, the separationunit for separating the reduced product from the solid reductant, andthe discharge unit for discharging the reduced product to the outside ofthe movable-hearth furnace may comprise a belt conveyor which opposesthe movable hearth at at least one part of the belt conveyor and extendsto the outside of the movable-hearth furnace, and at least one magnetwhich is provided within a circle formed by a belt of the belt conveyorat least at a position opposing the movable hearth and adjacent to theposition outside the movable-hearth furnace, the at least one magnetbeing for attracting the reduced product from the movable hearth,thereby separating the reduced product from the solid reductant.

[0026] The at least one magnet may either be disposed in a positionopposing the movable hearth with the belt of the belt conveyortherebetween, or be fixed to a rear face of the belt of the beltconveyor.

[0027] The removal unit for removing the reduced product from themovable hearth, the separation unit for separating the reduced productfrom the solid reductant, and the discharge unit for discharging thereduced product to the outside of the movable-hearth furnace maycomprise a first belt conveyor which opposes the movable hearth at atleast one part of the first belt conveyor and extends to the outside ofthe movable-hearth furnace, a second belt conveyor which is providedwithin a circle formed by a belt of the first belt conveyor and isdisposed at a position opposing the movable hearth with a lower part ofthe belt of the first belt conveyor therebetween, the rotation of thefirst belt conveyor and the second belt conveyor being substantiallysynchronized with each other, and at least one magnet which is mountedon a rear face of the belt of the second belt conveyor.

[0028] The discharging device according to the invention may furthercomprise a scraper disposed in the vicinity of a portion of the beltconveyor to which a magnetic force is not applied and which is outsidethe movable-hearth furnace, the scraper being for scraping the reducedproduct adhered to a front face of the belt of the belt conveyor.

[0029] The removal unit for removing the reduced product from themovable hearth and the separation unit for separating the reducedproduct from the solid reductant comprise a rotary drum which spans themovable hearth of the movable-hearth furnace in the widthwise directionof the movable hearth and is provided with at least one magnet at leastat a part of the rotary drum opposing the movable hearth, for attractingthe reduced product disposed on the movable hearth, and the dischargeunit for discharging the reduced product to the outside of themovable-hearth furnace comprises transfer unit which is disposed inparallel to the axis of the rotary drum, and which receives the reducedproduct attracted to and falling from the rotary drum and transfers thereduced product to the outside of the movable-hearth furnace.

[0030] The rotary drum may comprise an outer drum and an inner rollerwhich is disposed inside the outer drum and which is provided with theat least one magnet fixed to the cylindrical surface of the innerroller. The at least one magnet may extend in the rotational directionof the rotary drum from a lower part of the cylindrical surface to apart thereof associated with the discharge unit. The discharge unit maycomprise a belt conveyor which is disposed in parallel to the axis ofthe rotary drum, and which receives the reduced product attracted to andfalling from the rotary drum, and extends from the movable hearth to theoutside of the movable-hearth furnace.

[0031] The rotary drum may be provided with a plurality of protrusionson a peripheral face of the rotary drum. With this arrangement, thereduced product disposed on the movable hearth can be turned over sothat the metal included therein faces toward the magnet, whereby thereduced product can be reliably attracted and separated from the movablehearth and be easily separated from the rotary drum.

[0032] The rotary drum may be formed as a cylinder having a smallerdiameter at an intermediate part in the axial direction of the cylinder.With this arrangement, the solid reductant layer is prevented from beingdeformed at the sides of the movable hearth.

[0033] A cooling member may be provided for cooling the reduced productbefore the reduced product has a magnetic field applied thereto so as tobe attracted and removed from the movable hearth by the magnetic force.The attracting force of the magnet to the reduced product is preferablyincreased by cooling the reduced product to a given temperature which isnot higher than the Curie point. The same effect is obtainable when therotary drum is cooled, even when the reduced product has a temperatureabove the Curie point.

[0034] In the discharging device according to the invention, the removalunit for removing the reduced product from the movable hearth and theseparation unit for separating the reduced product from the solidreductant may comprise a classifying member including at least onenet-shaped or comb-shaped screen protruding from the periphery of a drumin a radial direction thereof, the drum spanning the movable hearth ofthe movable-hearth furnace in the widthwise direction of the movablehearth, and the discharge unit for discharging the reduced product tothe outside of the movable-hearth furnace may comprise a transferconveyor which transfers the reduced product scooped from the movablehearth by the classifying member.

[0035] The transfer conveyor may be disposed in the vicinity of the drumprovided with the classifying member and substantially parallel to theaxis of the drum, the transfer conveyor being disposed at a position inwhich the transfer conveyor receives the reduced product falling fromthe classifying member. The transfer conveyor may be disposed to passthrough the drum in the axial direction thereof, and the drum may beprovided with at least one opening formed in the drum in the vicinity ofthe net-shaped or comb-shaped screen such that the reduced productscooped by the at least one net-shaped or comb-shaped screen is receivedby the transfer conveyor through the at least one opening.

[0036] The discharging device according to the invention may furthercomprise side plates individually disposed at sides of the movablehearth along the direction of movement of the movable hearth, forpreventing a deposited substance from collapsing. The net-shaped orcomb-shaped screen may be provided with a bent part formed at an end(the free end) thereof.

[0037] The removal unit for removing the reduced product from themovable hearth, the separation unit for separating the reduced productfrom the solid reductant, and the discharge unit for discharging thereduced product to the outside of the movable-hearth furnace maycomprise a screw feeder which spans the movable hearth in the widthwisedirection thereof and extends to the outside of the movable-hearthfurnace, and a casing disposed at the downstream side of the screwfeeder in the direction of movement of the movable hearth, the casingbeing formed with a sidewall extending along the axis of the screwfeeder and a bottom plate extending from the sidewall substantially inparallel to the movable hearth.

[0038] The casing may be provided with a plurality of apertures. Thereduced product which has a grain size larger than that of the solidreductant can be separated from the solid reductant by using a screen.Therefore, the casing is preferably provided with apertures throughwhich the solid reductant having a smaller grain size can pass and thereduced product having a larger grain size cannot pass. A major portionof the solid reductant which enters between the screw feeder and thecasing passes through the apertures and falls onto the movable hearth atthe downstream side of the discharging device. The apertures may beformed in slits in the sidewall and/or the bottom plate of the casing,or a metallic net or the like which has mesh openings each havingsubstantially the same size as the aperture may be mounted on thecasing.

[0039] The removal unit for removing the reduced product from themovable hearth, the separation unit for separating the reduced productfrom the solid reductant, and the discharge unit for discharging thereduced product to the outside of the movable-hearth furnace maycomprise a screw feeder which spans the movable hearth in the widthwisedirection thereof, a reductant-discharging shooter disposed at aposition associated with an end part of the screw feeder protruding tothe outside of the movable-hearth furnace, a reduced-product-dischargingshooter disposed toward an outer side of the movable-hearth furnace fromthe reductant-discharging shooter, and a cylindrical screen which coversthe end part of the screw feeder associated with the position at whichthe reductant-discharging shooter is disposed, the rotation of thecylindrical screen being synchronized with that of the screw feeder. Thereduced-product-discharging shooter may be positioned at an open end ofthe cylindrical screen.

[0040] The removal unit for removing the reduced product from themovable hearth, the separation unit for separating the reduced productfrom the solid reductant, and the discharge unit for discharging thereduced product to the outside of the movable-hearth furnace maycomprise a guide plate disposed in a discharge section of the movablehearth, for reducing the width of an accumulative layer of the reducedproduct and the solid reductant, and a screw feeder disposed in adirection substantially perpendicular to the direction of movement ofthe movable hearth and provided with a tapered part toward a dischargeend of the screw feeder on the movable hearth, an end part of the screwfeeder from the tapered part to the end thereof protruding to theoutside of the movable-hearth furnace being formed as a reduced-diameterpart. A conical collecting shooter may be disposed at the tapered partof the screw feeder. A discharge cylinder may be disposed about thereduced-diameter part of the screw feeder toward the discharge endthereof from the conical collecting shooter. The discharge cylinder maybe provided with a net-shaped screen at a portion of the dischargecylinder associated with the movable hearth. Areduced-product-discharging shooter may be provided at an open end ofthe discharge cylinder disposed at the outside of the movable-hearthfurnace.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041]FIG. 1 is a perspective view of a known movable-hearth furnace;

[0042]FIG. 2 is a sectional view of a known discharging device;

[0043]FIG. 3 is a graph showing the relationship between the number oftimes of attraction and the temperature of reduced iron;

[0044]FIG. 4 is an illustration of reduced iron as a reduced product;

[0045]FIG. 5 is a sectional view showing a method for cooling thereduced iron by using a cooling plate;

[0046]FIG. 6 is a sectional view showing a method for cooling thereduced iron by spraying water;

[0047]FIG. 7 is a sectional view showing a method for directly coolingthe reduced iron;

[0048]FIG. 8 is an illustration of a discharging device according to theinvention;

[0049]FIG. 9 is an illustration of the discharging device according tothe invention;

[0050]FIG. 10 is an illustration of the discharging device according tothe invention;

[0051]FIG. 11 is an illustration of the discharging device according tothe invention;

[0052]FIG. 12 is an illustration of the discharging device shown in FIG.11, according to the invention;

[0053]FIG. 13 is an illustration of a rotary drum provided with magnetsdisposed along ¾ of the periphery of the rotary drum, rotating in adirection opposite to the movement of a movable hearth;

[0054]FIG. 14 is an illustration of the rotary drum provided withprotrusions for scraping;

[0055]FIG. 15 is an illustration showing a state in which discharge isnot performed smoothly;

[0056]FIG. 16 includes illustrations of a tapered drum;

[0057]FIG. 17A is a perspective view of a drum having a smaller diameterin a longitudinally intermediate part thereof;

[0058]FIG. 17B includes sectional views of the drum shown in FIG. 17A;

[0059]FIG. 18A is a sectional view of a portion of the movable hearth, asolid reductant layer formed on the movable hearth, and a material layerformed on the solid reductant layer;

[0060]FIG. 18B is a perspective view of a portion of the movable hearth,the solid reductant layer, and the material layer shown in FIG. 18A;

[0061]FIG. 19A is a sectional view of a portion of the movable hearth,the solid reductant layer on the movable hearth, and a reduced producton the solid reductant layer;

[0062]FIG. 19B is a perspective view of a portion of the movable hearth,the solid reductant layer, and the reduced product shown in FIG. 19A;

[0063]FIG. 20A is an illustration of a selector used in the dischargingdevice according to the invention;

[0064]FIG. 20B is an illustration of another selector used in thedischarging device according to the invention;

[0065]FIG. 20C is a cross-sectional view of the selector shown in FIG.20B;

[0066]FIG. 21A is an illustration of a discharging device according toan embodiment of the invention;

[0067]FIG. 21B is an illustration of a discharging device according toanother embodiment of the invention;

[0068]FIG. 22 is an illustration of a discharging device according toanother embodiment of the invention;

[0069]FIG. 23 is a perspective view of the discharging device shown inFIG. 22;

[0070]FIG. 24 is an illustration showing a discharge operation in whichthe reduced product is loaded onto a transfer conveyor passing through arotary drum;

[0071]FIGS. 25A, 25B, 25C, and 25D are illustrations showing the solidreductant layer being deformed with the movement of a screen;

[0072]FIG. 26 is an illustration showing the function of side plates foravoiding deformation of the solid reductant layer;

[0073]FIG. 27 is a perspective view of guide plates for correcting thewidth of the solid reductant layer;

[0074]FIG. 28 is an illustration of a discharging device according toanother embodiment of the invention;

[0075]FIG. 29 is an illustration of the discharging device shown in FIG.28;

[0076]FIG. 30 is an illustration of the discharging device shown in FIG.29;

[0077]FIG. 31 is an illustration of a discharging device according toanother embodiment of the invention;

[0078]FIG. 32 is an illustration of a discharging device according toanother embodiment of the invention;

[0079]FIG. 33 is a sectional view of a discharging device according toanother embodiment of the invention;

[0080]FIG. 34 is a sectional view of a discharging device according toanother embodiment of the invention; and

[0081]FIG. 35 is a perspective view of a guide plate for reducing thewidth of a layer including the reduced product and the solid reductant.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0082] A movable-hearth furnace and a discharging method according toembodiments of the invention are described below.

[0083] As shown in FIGS. 18A and 18B, when operating a movable-hearthfurnace, a solid reductant layer 1 b is formed on a movable hearth 11, amixed raw material 12 (from FIG. 1) including as major components aniron-containing substance and a solid reductant (mixed solid reducingagent) is deposited to form a raw-material layer 1 a on the solidreductant layer 1 b, and the raw-material layer la is heated bycombustion of a burner 13 (from FIG. 1) disposed in an upper part of themovable-hearth furnace, whereby the iron-containing substance in themixed raw material 12 is reduced by an action of the solid reductantincluded in the mixed raw material 12, a reduced product 16 (from FIG.2) including gangue and the like is produced, and ash included in thesolid reductant is separated from the solid reductant. In this case, thevolume of the reduced product 16 is smaller by far than that of themixed raw material 12 because the solid reductant is consumed with thereaction, although the difference in volume between the reduced product16 and the mixed raw material 12 differs according to the method ofblending and the composition of the mixed raw material 12. Asub-material which accelerates melting of the reduced product 16 and theash is added to the mixed raw material 12. The mixed raw material 12 ismaintained in a solid state after reduced and until melted althoughvaporization of crystal water and a decomposition reaction occur (forexample, CaCO₃ as a major component of a limestone is pyrolyzed to CaO).When the mixed raw material 12 in a solid state is further heated, theiron-containing substance, the ash, and the sub-material start to bemelted, and a metal and slag are separated to be produced. In this case,since the mixed raw-material layer 1 a which is a mixture of theiron-containing substance and the solid reductant, or theiron-containing substance, the solid reductant, and the sub-material isdeposited on the solid reductant layer 1 b, a metal 2 and slag 3 shownin FIGS. 19A and 19B are produced to be disposed on the solid reductantlayer 1 b. The solid reductant layer 1 b, although it is an accumulativelayer of a reductant, does not include metal-containing substance.Therefore, it does not practically function as a reductant and does notchemically change except for a portion which vaporizes during operation.Generally, the solid reductant includes ash of approximately 10 percentand a carbonaceous substance as a major part for the remaining portion.The solid reductant layer 1 b is maintained in a solid state whenexposed to a high temperature on the order of 1000 to 1500° C.Therefore, the solid reductant layer 1 b does not adhere to aheat-resistive material disposed on the surface of the movable hearth11, whereby the solid reductant layer 1 b can be used as a protectivelayer for the heat-resistive material.

[0084] A plurality of concavities 46 as shown in FIGS. 18A and 18B maybe formed in the solid reductant layer 1 b, as shown in FIGS. 19A and19B, and the mixed raw material 12 which forms the raw-material layer 1a is disposed on the solid reductant layer 1 b provided with theplurality of concavities 46. When the mixed raw material 12 is reducedand heated, and thereby melted, the melted metal and slag agglomerate inthe concavities 46 formed in the solid reductant layer 1 b by the effectof surface tension and gravity of the melted metal and slag, whereby themetal 2 with the slag 3 is divided into units in the concavities, asshown in FIGS. 19A and 19B.

[0085] Since the melted metal 2 and the slag 3 have a volume percent ofonly about 10 to 60% of the mixed raw material 12, each unit of themelted metal 2 with the slag 3 agglomerating in the concavity 46 can beseparated from the other units formed in adjacent concavities 46. Thespecific gravities of the melted metal 2 and the slag 3 are generallygreater than that of the solid reductant. Therefore, there is a riskthat the melted metal 2 and the slag 3 will move into and/or under thesolid reductant layer 1 b. However, when the mixed raw material 12,which is a mixture of the metal-containing substance and the solidreductant or the sub-material added thereto, and is disposed on thesolid reductant layer 1 b provided the concavities 46 therein, isreduced and is melted, the melted metal 2 with the slag 3 isagglomerated by being sustained in each of the concavities 46 in thesolid reductant layer 1 b by the effect of surface tension.

[0086] When the melted metal 2 with the slag 3 separated from the gangueand ash and disposed on the solid reductant layer 1 b is cooled in acooling zone 10 d on the movable hearth 11 shown in FIG. 1, and themelted metal 2 with the slag 3 agglomerates in each of the concavities46. The agglomerated metal 2 with slag 3 in each concavity 46 ismaintained to be separated from the movable hearth 11 with the solidreductant layer 1 b therebetween.

[0087] The grain diameter of the solid reductant included in the solidreductant layer 1 b is preferably not larger than approximately 8 mm,because there is a risk that the melted metal 2 and slag 3 willinfiltrate the solid reductant layer 1 b and reach the heat-resistivematerial disposed on the hearth 11 when the grain diameter of the solidreductant is larger.

[0088] Since the solid reductant in the solid reductant layer 1 b on thehearth 11 does not significantly contribute to the reduction reaction,as described above, it is not likely to be oxidized and carburized.Therefore, the solid reductant remaining on the hearth 11 can berecycled. The whole of the solid reductant may be discharged andselected at the outside of the furnace. However, the solid reductantimmediately after being discharged is very hot and dangerous because ofthe risk of fire when being sifted outside the furnace. On the otherhand, when the solid reductant is reloaded while it is hot or the solidreductant is left in the furnace, the sensible heat of the solidreductant can be used efficiently. Therefore, the reduced product 16which has a larger grain size is preferably selectively collected on thehearth 11 of the furnace and the solid reductant having a smaller grainsize is preferably left in the furnace to be used as the solid reductantlayer 1 b.

[0089] According to an embodiment of the invention, the reduced product16 including reduced iron pellets, metals, and slag is attracted andremoved from the movable hearth 11 by using a magnetic force of amagnet, and is transferred and discharged to the outside of the furnacefor collection. Because the reduced product 16 produced on the movablehearth 11 is attracted and lifted, thereby removing it from the surfaceof the movable hearth 11, by using a magnet, the reduced product 16 canbe discharged smoothly without scratching the heat-resistive material onthe movable hearth as in known methods. Because a magnet is used, only ametal with slag attracted to the magnet can be selectively dischargedeven when the metal with slag is produced by the technology disclosedin, for example, Japanese Unexamined Patent Application Publication No.11-172312, and the solid reductant which is not affected by the magneticforce of the magnet can be completely left on the hearth 11 except for avery small portion of the solid reductant adhered to the metal and slag.The solid reductant can be reused with the raw materials loaded thereonin the subsequent step.

[0090] A method for discharging the reduced product from themovable-hearth furnace according to the invention is described below.

[0091] The magnetization of iron decreases at high temperature. Inparticular, it is known that iron has substantially no magnetism at atemperature above the Curie point. We performed a test in which themanufactured reduced product 16 was heated in an electric furnace andattracted by a magnet at different temperatures. In the test, thereduced product 16 was brought into contact with a magnet of 0.1 T tentimes for two seconds per contact. The number of times at which thereduced product 16 was attracted by the magnet are shown in FIG. 3. Arepresentative illustration of the reduced product 16 which was used inthe test is shown in FIG. 4. The reduced product 16 including the metal2 with the slag 3 having a grain size approximately the same as thelargest grain size of a reduced product generally produced by amovable-hearth furnace was used because the reduced product having asmaller size could be more easily attracted. The reduced product 16 wasattracted several times at a furnace temperature of 900° C., as shown inFIG. 3. The fact may be because the surface temperature of the reducedproduct 16 which was reduced iron decreased due to the magnet, which wasat room temperature, coming into contact with the reduced product 16 inthe furnace, whereby the reduced iron was magnetized in the vicinity ofthe surface thereof and the attraction was possible even when thefurnace temperature was above the Curie point.

[0092] The reduced iron can be attracted by decreasing the temperatureof the magnet below the Curie point. It is apparent that at least thereduced product 16 is preferably cooled.

[0093] The temperature of the reduced product 16 is decreased in such apreferable manner that the reduced product 16 is cooled to a propertemperature before a magnetic field is applied to the reduced product16. For example, a cooling plate 17 mounted therein with a cooling pipe17 a is provided at an upper part of the hearth 11, and the reducedproduct is cooled by heat radiation to the cooling plate 17, as shown inFIG. 5. In FIG. 6, a coolant-dispersing device 18 sprays water, an inertgas, or the like for cooling from above the hearth 11. In FIG. 7, acooling drum 19 is provided for directly cooling the reduced iron, whichis advantageous because the reduced iron which has higher thermalconductivity than slag or solid reductant can be selectively cooled.However, although it is advantageous that the reduced iron can beselected by attraction to be collected by decreasing the temperature ofthe reduced iron for collection, there is a problem in that heat loss isunnecessarily increased, thereby reducing the thermal efficiency of thefurnace. The magnetic force is effective to the reduced product 16 whichis reduced iron even when the temperature thereof is in a range of notlower than the Curie point (approximately 800° C.) and not higher thanabout 900° C.

[0094] Another test was performed to study the effect of the slag 3adhered to the metal 2. In that test, the effect of the slag 2 onattraction when the metal 2 of the reduced product 16 was disposedupward was confirmed. As a result, when the metal 2 was upwardlydisposed (see FIG. 13), the reduced product 16 could be collected at ahigh collection rate. It was believed that the attractive forceincreased with the metal 2 being directly in contact with a magnet 5.Therefore, it is desirable that the distance between the magnet 5 andthe metal 2 of the reduced product 16 is reduced to a minimum, therebyincreasing the attractive force. Therefore, the magnet 5 is preferablyheld substantially vertically movable so that the distance can becontrolled.

[0095] The discharging method and the discharging device according tothe present invention are further described below in detail withreference to the drawings.

[0096]FIG. 8 shows a discharging device according to the invention. Thedischarging device discharges the reduced product 16 including the metal2 and the slag 3 formed on the solid reductant layer 1 b. Thedischarging device shown in FIG. 8 includes as a major component a beltconveyor 4 which is disposed above the movable hearth 11 and of whichthe transfer direction is substantially perpendicular to the directionof movement of the movable hearth 11, the belt conveyor 4 extending tothe outside of the furnace. The belt conveyor 4 is provided with amagnet 5 at a position 4 a opposing the movable hearth 11 and at aposition 4 b disposed outside the furnace and adjacent the position 4 a,the magnet 5 serving to generate a magnetic force for attracting thereduced product 16 including the metal 2 and the slag 3 produced on themovable hearth 11. The magnet 5 is affixed above the movable hearth 11to oppose the same with a belt 40 of the belt conveyor 4 therebetween.

[0097] When the belt 40 of the belt conveyor 4 shown in FIG. 8 is drivenin a direction R, the reduced product 16 including the metal 2 and theslag 3 produced on the solid reductant layer 1 b is attracted to thebelt 40 by the magnetic force of the magnet 5, whereby the reducedproduct 16 is separated from the movable hearth 11, is adhered to thebelt 40, and is moved with the belt 40 in the rotational direction. Themetal 2 and the slag 3 are attracted and adhered to the belt 40 at leastat the position 4 a opposing the movable hearth 11 and the position 4 boutside the furnace.

[0098] The metal 2 and the slag 3, which have been transferred with themovement of the belt 40 to a region outside the furnace in which themagnet 5 is not provided, fall down by their own weight because theattractive force of the magnet 5 is discontinued or not applied outsideof the furnace. Thus, the metal 2 and the slag 3 on the movable hearth11 are raised from the movable hearth 11 by the magnet 5, and aretransferred and discharged to the outside of the furnace.

[0099] A material which transmits a magnetic force, such as a typicalrubber belt, an austenitic stainless steel, or the like may be used forthe belt conveyor 4 described above. In particular, when a metallic beltmade of a material, such as an austenitic stainless steel is used, thereduced product 16 can be removed from the movable hearth 11 by using amagnetic force when the temperature of the reduced product 16 decreasesbelow the Curie point, although not too near room temperature, at whichtemperature iron included in the reduced product 16 has high magnetism.Therefore, in ordinary manufacture of reduced iron, the reduced product16 can be discharged at a temperature ranging from about 500 to about600° C. That is, costs of energy can be reduced when sensible heat iscollected from a product at the outside of the furnace or the product ismelted in the subsequent process.

[0100] The discharging device described above is preferably providedwith a scraping plate 6 at the downstream side, from the region in whichthe magnet 5 is disposed, in the direction of transfer by the beltconveyor 4, the scraping plate 6 being for removing the metal 2 and theslag 3 adhering to the belt 40.

[0101] The magnet 5 may be either a permanent magnet or an electromagnetand may consist of multiple smaller magnets. The strength of magneticforce of the magnet 5 may be appropriately set according to thecharacteristics of the metal and slag to be produced and the distancebetween the belt conveyor 4 and the surface of reductant layer 1 b. Inparticular, the strength of magnetization of the magnet 5 and the heightof the conveyor 4 are controlled for each installation so that themagnetic flux density is on the order of about 0.1 to about 0.2 T at thesurface of the belt conveyor 4, and are set according to the dischargedstate of the product. When using an electromagnet as the magnet 5, anappropriate discharge condition can be determined by controlling thecurrent applied to the electromagnet.

[0102] A discharging device shown in FIG. 9 includes magnets 5 mountedon the entire rear face of the belt 40 of the belt conveyor 4. In thedischarging device, the metal 2 and the slag 3 adhering to the frontface of the belt 40 are scraped by the scraper 6 at the outside of thefurnace. The belt 40 and the magnet 5 of the discharging device shown inFIG. 9 are basically the same as those of the discharging device shownin FIG. 8.

[0103] A discharging device shown in FIG. 10 differs from thedischarging device shown in FIG. 8 which is provided with the magnet 5in the vicinity of a lower belt of the belt conveyor 4, in that abuilt-in belt conveyor 41 is provided between upper and lower belts ofthe belt conveyor 4 to oppose the movable hearth 11 and move in thewidthwise direction of the movable hearth 11, the built-in belt conveyor41 being provided with magnets 5 directly fixed to the inner face of abelt of the built-in belt conveyor 41. The built-in belt conveyor 41 isdriven substantially at the same speed as and synchronized with the beltconveyor 4 which encloses the built-in belt conveyor 41. The metal 2 andthe slag 3 on the movable hearth 11 are attracted by the magnets 5mounted to the rear face of the built-in belt conveyor 41, in the samemanner as shown in FIG. 8, are transferred by being attracted to a belt40 of the belt conveyor 4, and are discharged to the outside of thefurnace, as shown in FIG. 10.

[0104] In the discharging device shown in FIG. 10, the belt 40 is notnecessarily made of a stainless steel even when the reduced product 16is hot, and it may be an ordinary metallic belt. When a steel belt whichis attracted by a magnet is used in the discharging device shown in FIG.8, the belt conveyor 4 cannot smoothly operate due to the attractionbetween the steel belt and the magnet 5. On the other hand, in thedischarging device shown in FIG. 10, the belt conveyor 4 can operatesmoothly because the magnets 5 and the steel belt move at the same speedas each other.

[0105] Although in the discharging device according to the embodimentsdescribed above, the reduced product 16 which is discharged from themovable hearth 11 includes the metal 2 and the slag 3, the reducedproduct 16 may include reduced iron pellets. In the discharging deviceto be described below, the reduced product 16 may also include thereduced iron pellets.

[0106] Although the discharging device according to the above-describedembodiments uses a belt conveyor, a discharging device according toanother embodiment of the present invention uses a rotary drum providedwith magnets, as shown in FIG. 11. The discharging device is provided asa major component with a rotary drum 7 which spans the movable hearth11. The rotary drum 7 is mounted with magnets 5 at least in one part ofthe rotary drum 7 opposing the movable hearth 11.

[0107] As shown in FIGS. 11 and 12, the rotary drum 7 includes acylindrical inner roller 7 a provided with the magnets 5 fixed to theouter face of the inner roller 7 a, and an outer drum 7 b which isrotatable coaxially with the inner roller 7 a and is separated from theinner roller 7 a via bearings 7 c, the inner roller 7 a being disposedinside the outer drum 7 b. The outer drum 7 b rotates in the directionof movement of the movable hearth 11. In FIG. 12, a drive chain 7 drotates the outer drum 7 b.

[0108] The reduced product 16 including a metal and the like which isattracted by the magnets 5 and is removed from the movable hearth 11 istransferred by a transfer conveyor 8 and collected at the outside of thefurnace. The magnets 5 are fixed to the outer face of the inner roller 7a in a part of the rotary drum 7 opposing the movable hearth 11, towardan intermediate part of the inner roller 7 a from a lower part thereof.The transfer conveyor 8 is disposed in parallel to the axis of therotary drum, and which receives the reduced product attracted to andfalling from the rotary drum, and extends from the movable hearth to theoutside of the movable-hearth furnace. The transfer conveyor 8 includesa belt conveyor for discharge, which extends from the movable hearth 11to the outside of the furnace.

[0109] When the rotary drum 7 rotates in a direction opposite to thedirection of movement of the movable hearth 11, the magnets 5 arepreferably mounted to approximately ¾ of the area of the outer face ofthe cylindrical inner roller 7 a in a rotational direction of the rotarydrum 7. The reduced product 16, which is attracted to the outer drum 7 band revolves about the inner roller 7 a, falls down onto the transferconveyor 8 because the magnetic force ceases to be applied to thereduced product 16 above the transfer conveyor 8.

[0110] By thus appropriately setting the temperature of the reducedproduct 16 and the position of the magnets 5, the maximum strength ofmagnetic field applied to the rotary drum 7 can be decreased, whereby itis not necessary to use a costly magnet such as a superconductingmagnet, thereby reducing the manufacturing cost of the dischargingdevice.

[0111] The rotational direction of the rotary drum 7 is preferablyopposite to the direction of movement of the movable hearth 11. With therotary drum 7 rotating in a direction opposite to the direction ofmovement of the movable hearth 11, the reduced product 16 once attractedto the rotary drum 7 and removed therefrom can be collected by beingbrought again into contact with the rotary drum 7, whereby theefficiency in collection can be improved.

[0112] The outer drum 7 b is preferably positioned to have a clearance t(t=10 to 20 mm) from the magnets 5 which are fixed to the inner roller 7a, so as not to come into contact with the magnets 5. The metal 2 andthe slag 3 produced on the movable hearth 11 are removed from themovable hearth 11, attracted to the surface of the outer drum 7 b by amagnetic force, transferred in the rotational direction of the outerdrum 7 b, separated from the surface of the outer drum 7 b by their ownweight when they reach a portion in which the magnets 5 are notprovided, and fall down onto the transfer conveyor 8.

[0113] The transfer conveyor 8 is a belt conveyor which circulates alongthe axis of the outer drum 7 b and in a direction substantiallyperpendicular to the direction of movement of the movable hearth 11 andtransfers the reduced product 16 to the outside of the furnace. The beltconveyor may be an ordinary rubber belt or a heat-resistive metallicbelt when it is used when the temperature of the reduced product 16 ishigh.

[0114] The inner roller 7 a must only have strength enough for affixingthe magnets 5 on the surface thereof, and the material for the innerroller 7 a is not limited to a particular material. The outer drum 7 bwhich transmits a magnetic force and rotates is preferably made of anon-magnetic metal such as an austenitic stainless steel. The outer drum7 b may be provided with a friction-resistive liner on the surfacethereof.

[0115] The magnets 5 may be either permanent magnets or electromagnets.A magnetic flux density of approximately 0.2 T at the surface of theouter drum 7 b is required. The magnetic strength of the magnets 5 andthe distance between the surface of the outer drum 7 b and thesubstances on the movable hearth 11 to be attracted may be controlledfor each installation and determined in accordance with the dischargedstate of the product.

[0116] The reduced product 16 attracted to the surface of the outer drum7 b at a portion thereof associated with the magnets 5 is not likely tobe removed therefrom. In order to avoid this phenomenon, a plurality ofprotrusions 20 or 23 are preferably provided on the peripheral surfaceof the outer drum 7 b, as shown in FIG. 14 or FIGS. 17A and 17B,respectively, whereby the attracted metal 2 and the like become easy tobe removed from the surface of the outer drum 7 b. Moreover, the reducedproduct 16 disposed on the movable hearth 11 is turned over by theprotrusions 20 or 23 and the metal 2 included in the reduced product 16faces upward, whereby the magnetic force of the magnets 5 can be usedeffectively, as shown in FIG. 3, thereby further improving collectionefficiency.

[0117] The rotary drum 7 may be brought into contact with the solidreductant layer 1 b for collection of the metal 2 and the like when therotary drum 7 including the magnets 5 is sufficiently cooled. However,there is a risk that solid reductant from the solid reductant layer 1 bnot to be discharged is accumulated at the leading side of the rotarydrum 7 by the resistance of the rotary drum 7, thereby blocking theoperation of the rotary drum 7, when the rotary drum 7 without theprotrusions 20 and 23 are pressed into a layer of raw materials, asshown in FIG. 15.

[0118] Accordingly, in order to solve the above problem, a rotary drum21 having a tapered cylindrical 20 body according to another embodimentof the invention is provided, as shown in FIG. 16. With thisarrangement, the solid reductant layer 1 b as asolid-reductant-accumulated layer pressed by the tapered cylindricalsurface of the rotary drum 21 moves toward the side at which thediameter of the rotary drum 21 is smaller as long as a gap large enoughfor the solid reductant layer 1 b to pass through is provided betweenthe movable hearth 11 and the rotary drum 21, whereby the solidreductant layer 1 b can be prepared without deformation thereof for rawmaterials to be charged in the subsequent step.

[0119] Since the solid reductant included in the solid reductant layer 1b is reused on the movable hearth 11, the reductant layer 1 b ispreferably left as it was used in the preceding step. However, the solidreductant layer 1 b is deformed when the reduced product 16 such asreduced iron (metal) and the like is collected, whereby the raw-materiallayer 1 a is deformed and, sometimes, the solid reductant falls from themovable hearth 11.

[0120] A modified example of the above-described rotary drum 21 having atapered cylindrical body is shown in FIGS. 17A and 17B. The modifiedexample includes a roller 22 having a smaller diameter at alongitudinally intermediate part thereof. With this arrangement, thesolid reductant of the solid reductant layer 1 b moves toward anintermediate part in the widthwise direction of the movable hearth 11 sothat the solid reductant layer 1 b becomes thicker at the widthwiseintermediate part thereof, whereby the deformation of the solidreductant layer 1 b can be reliably avoided. The function of theprotrusions 23 of the modified rotary drum 21 is the same as that of theprotrusions 20 of the rotary drum 7 shown in FIG. 14.

[0121] According to another embodiment of the invention, a method forclassifying a reduced product according to its grain size anddischarging the reduced product having a larger grain size to theoutside of a furnace for collection by using a device is describedbelow.

[0122] The grain size of the metal 2 and slag 3 is larger than the grainsize of the solid reductant included in the solid reductant layer 1 b,as described above. Therefore, separation of the metal 2 (reduced iron)and slag 3 from the solid reductant included in the solid reductantlayer 1 b according to the grain size is made possible.

[0123] Therefore, the metal 2 and slag 3 as a product preferably have agrain size not smaller than about 10 mm. Generally, the grain size of ametal with slag becomes about 10 mm or larger by the effect of surfacetension when the metal and slag agglomerate in a movable-hearth furnace.However, since the grain size of the metal with slag is sometimes notlikely to become about 10 mm or larger only by depositing and meltingraw materials, the concavities 46, described above, each having adiameter of not less than about 10 mm are provided in the solidreductant layer 1 b such that the metal with slag has a grain size ofnot less than about 10 mm.

[0124] The metal with slag having a smaller grain size and not capableof being separated from the solid reductant are left on the hearth andheated and melted together with the raw materials charged in thesubsequent step, and can be collected as the reduced product 16 having alarger grain size.

[0125] The device to be used in the discharging method is describedbelow. The device includes a selector and a transfer conveyor. Aselector S is shown in FIGS. 20A, 20B, and 20C, of which a majorcomponent is the rotary drum 7. The rotary drum 7 spans the movablehearth 11 at a discharge section thereof positioned at the downstreamside of a cooling zone 10 d of the furnace. The rotary drum 7 isprovided with a plurality of net-shaped screens 41 or comb-shapedscreens 42, each protruding radially outwardly from the rotary drum 7from the periphery thereof. With the rotation of the rotary drum 7, thescreens 41 or 42 scoop only the reduced product 16 including metal,slag, and reduced pellets having a larger grain size of, for example,not smaller than about 5 mm from the reduced product 16 scattered on thesolid reductant layer 1 b on the movable hearth 11, and leave the solidreductant 65 having a smaller grain size on the hearth 11.

[0126] Each screen 41 or 42 is preferably provided with a hook 42 a,which is bent or oriented toward the leading side of the rotation, at anend (the free end) of the screen 41 or 42. FIG. 21A and 21B show theselector S in operation. The transfer conveyor 8 is provided adjacentthe selector S for discharging the reduced product 16 to the outside ofthe furnace. FIG. 21A shows the transfer conveyor 8 movable in asubstantially horizontal direction. FIG. 21B shows the transfer conveyor8 provided with magnets.

[0127] The transfer conveyor 8 shown in FIG. 21A is movable along arrowsshown in the drawing to avoid interference with the screens 42, thetransfer conveyor 8 moving substantially horizontally synchronized withthe position of the screens 42. That is, when the reduced product 16falls down from one of the screens 42, as shown in FIG. 21A, thetransfer conveyor 8 is positioned in the vicinity of the rotary drum 7to receive the falling reduced product 16. When the screen 42 revolvesto a position at which it interferes with the transfer conveyor 8, thetransfer conveyor 8 moves to the right in the drawing so thatinterference is avoided.

[0128] The transfer conveyor 8 shown in FIG. 21B is provided withmagnets disposed on the rear face of the transfer conveyor 8. When thereduced product 16 scooped by the screen 42 reaches an upper part of therotary drum 7, the reduced product 16 is attracted to the transferconveyor 8 by the magnets provided on the rear face of the transferconveyor 8, and discharged to the outside of the furnace with theoperation of the transfer conveyor 8. In this case, the rotary drum 7 ismade of a paramagnetic material such as an austenitic stainless steelsuch that the rotary drum 7 is not affected by the magnetic force.

[0129]FIGS. 22 and 23 show a combination of the selector S with thetransfer conveyor 8, according to another embodiment of the invention.In the embodiment, the transfer conveyor 8 is disposed to pass throughthe cylindrical rotary drum 7 in the axial direction thereof. The rotarydrum 7 is provided with openings 43 formed therein through which thereduced product 16 scooped by the screens 41 or 42 falls onto thetransfer conveyor 8.

[0130] The transfer conveyor 8 extends along the axis of the rotary drum7 to the outside of the furnace and synchronized with the rotation ofthe rotary drum 7 along the arrow in FIG. 23. Thus, the reduced product16 including reduced iron and slag which is selected on the hearth 11 isseparated from the solid reductant of the solid reductant layer 1 b anddischarged from the furnace.

[0131]FIG. 24 is a schematic view showing the operation of the rotarydrum 7 and the movement of the reduced product 16, according to theembodiment. As the rotary drum 7 rotates, the comb-shaped screen 42enters into the solid reductant layer 1 b and raises the reduced product16 including the metal 2 formed by reduction. When the reduced product16 reaches the upper part of the rotary drum 7, the reduced product 16falls through the opening 43 onto the transfer conveyor 8 disposed topass through the rotary drum 7, and is transferred and discharged to theoutside of the furnace by the transfer conveyor 8.

[0132] When using the rotary drum 7, the solid reductant layer 1 b maybe deformed by the resistance of the reduced product 16 to the screens41 or 42, which is described with reference to FIGS. 25A, 25B, 25C, and25D. The reduced product 16 is disposed on the solid reductant layer 1 bbefore the reduced product 16 is raised by the screens 41 or 42 of therotary drum 7, the solid reductant layer 1 b being formed flat at theupper part and to have a repose angle at each side face, as shown inFIG. 25B. When the screens 41 or 42 of the rotary drum 7 enter into thesolid reductant layer 1 b for scooping the reduced product 16, the solidreductant layer 1 b rises with the resistance thereof to the screens 41or 42 and is deformed at ends thereof in the widthwise direction of thehearth 11, as shown in FIG. 25C. Therefore, the solid reductant layer 1b becomes wider and thinner after the reduced product 16 is collected,as shown in FIG. 25D. The solid reductant forming the solid reductantlayer 1 b may reach one of the widthwise ends of the movable hearth 11and fall therefrom. When the solid reductant falls, it may produce aresistance to the movement of the movable hearth 11 to cause, in a worstcase, suspension of the operation thereof.

[0133] In order to avoid the deformation of the solid reductant layer 1b, side plates 44 may be provided extending in the direction of movementof the hearth 11 such that the screens 41 or 42 pass between the sideplates 44, as shown in FIG. 26. With this arrangement, the deformationof the solid reductant layer 1 b can be suppressed to a minimum, and thesolid reductant can be prevented from moving toward the widthwise endsof the hearth 11.

[0134] Since the width of the solid reductant layer 1 b is increased, asthe reduced product 16 is collected, even when the deformation of thesolid reductant layer 1 b can be avoided, the width of the solidreductant layer 1 b is preferably corrected by using guide plates 45extending in the direction of movement of the movable hearth 11, asshown in FIG. 27.

[0135] The temperature in the furnace increases to 1500° C. or higher onthe movable hearth 11 and to approximately 1000° C. on average at aposition at which the reduced product 16 is collected. Therefore,wearing of the screens 41 or 42 fixed to the rotary drum 7 issignificant due to the high temperature. Accordingly, the device ispreferably cooled. For example, a cooling mist is applied to the screens41 or 42 of the rotary drum 7, or cooling water is circulated throughpassages formed in the drum body and/or the screens 41 or 42 of therotary drum 7, whereby the durability of the device can be increased andthe time required for repairs can be decreased, thereby improving theoperating rate of the device.

[0136] With reference to FIGS. 28 to 32, another embodiment of thedischarging device according to the invention is described below.

[0137]FIG. 28 is an illustration of a discharging device according tothe embodiment of the invention. The discharging device includes a screwfeeder 53 and a casing 56. The screw feeder 53 spans the movable hearth11 substantially perpendicular to the direction of movement of themovable hearth 11 and extending to the outside of the furnace.

[0138] In FIG. 29, the casing 56 includes a sidewall 54 which extendsalong the axis of the screw feeder 53 and covers the screw feeder 53 atat least one side thereof toward the downstream side of the movablehearth 11, and a bottom plate 55 which extends under the screw feeder 53from the lower end of the sidewall 54 and substantially in parallel tothe movable hearth 11.

[0139] The screw feeder 53 is formed with a rod 53 a provided with aspiral screw 53 b about the rod 53 a. The spiral screw 53 b moves thereduced product 16 by being driven by a motor 53 c via the rod 53 a,thereby transferring the reduced product 16 to the outside of thefurnace.

[0140] While being moved by the spiral screw 53 b, the reduced product16 is likely to be clamped between the screw 53 b and the solidreductant layer 1 b, whereby the reduced product 16 is embedded into thesolid reductant of the solid reductant layer 1 b disposed on the movablehearth 11.

[0141] Therefore, the discharging device is provided with the sidewall54 which extends along the axis of the screw feeder 53 and covers thescrew feeder 53 at at least one side thereof toward the downstream sideof the movable hearth 11, and the bottom plate 55 which extends underthe screw feeder 53, substantially parallel to the movable hearth 11,and at a given distance therefrom. The casing 56 is open toward theupstream side of the movable hearth 11.

[0142] When the reduced product 16 is disposed in the solid reductantlayer 1 b, the bottom plate 55 of the casing 56 is lowered to the levelof the reduced product 16 embedded in the solid reductant layer 1 b byvertically moving the casing 56 which receives the screw feeder 53,whereby the reduced product 16 is scooped by the bottom plate 55 and issent into the screw 53 b instead of being depressed under the screw 53b.

[0143] The casing 56 may be vertically moved by a screw jack or amechanism driven by a force using oil pressure, an electric force,pneumatic pressure, or the like.

[0144] In this case, a space A defined by the sidewall 54, the bottomplate 55, and the screw 53 b is filled with the solid reductant of thesolid reductant layer 1 b when the screw feeder 53 starts to operate, asshown in FIG. 30. The solid reductant remains in the space A and is nottransferred even after the screw 53 b starts to rotate. Therefore, thereduced product 16 sent into the screw 53 b as the screw 53 b rotates istransferred toward the outside without being sent into the space A dueto the solid reductant remaining therein and is discharged from anoutlet 55 a formed in an end of the bottom plate 55 disposed outside themovable-hearth furnace.

[0145] The reduced product 16 disposed in an upper part of the solidreductant layer 1 b can be reliably sent into the screw 53 b of thescrew feeder 53, without being embedded into the solid reductant layer 1b, by a virtue of the bottom plate 55 of the casing 56, whereby almostthe entire reduced product 16 can be collected and discharged.

[0146] The width of the bottom plate 55 is preferably set in such amanner that a distance L from the end of the bottom plate 55 at theupstream side of the movable hearth 11 to the perpendicular line betweenthe bottom plate 55 and the axis of the screw 53 b is set to a valueabout 0.2 to about 0.3 times a radius R of the screw 53 b. When thedistance L is smaller than this value, the reduced product 16 passesunder the bottom plate 55. When the distance L is larger than thisvalue, the reduced product 16 and the solid reductant are excessivelyraised before reaching the screw 53 b and fall from the sides of themovable hearth 11.

[0147] A clearance t between the bottom plate 55 and the movable hearth11 is set according to the position of the reduced product 16 above themovable hearth 11. The clearance t may be set during operation whileconfirming a discharged state of the reducing product 16 so that thereduced product 16 can be discharged substantially completely. Athickness T of the solid reductant layer 1 b is preferably at leastapproximately 50 mm. When the thickness T is smaller, the entire solidreductant layer 1 b is moved by the bottom plate 55 and discharged morethan it is necessary.

[0148] The solid reductant layer 1 b between the bottom plate 55 and themovable hearth 11 after the reduced product 16 is removed is left on themovable hearth 11. The solid reductant and the raw materials arecharged, heated, and melted in the subsequent step. That is, the solidreductant left on the movable hearth 11 is recycled and reusedefficiently.

[0149] The reduced product 16 used in the above-described embodimentsincludes metals, slag, and reduced iron pellets.

[0150] When the reduced iron pellets are disposed directly on themovable hearth 11, the bottom plate 55 of the casing 56 is lowered suchthat the bottom plate 55 is brought into contact with the movable hearth11 (such that the clearance t becomes substantially zero), whereby thereduced iron pellets are substantially completely discharged.

[0151] In this case, the space A is also filled with the reduced ironpellets when the screw feeder 53 starts to operate. Thereafter, thereduced iron pellets can be substantially completely discharged by usingone screw feeder 53.

[0152] With reference to FIGS. 31 and 32, a modified example of thedischarging device is described below, of which the casing 56 isprovided with apertures. The sidewall 54 of the casing 56 shown in FIGS.31 and 32 is provided with a plurality of apertures 51 each extendingvertically and at a uniform distance from others. The size of eachaperture 51 is smaller than the grain size of the reduced product 16,whereby the reduced product 16 can be selectively discharged. Forexample, when the grain size of the reduced product 16 is set to about 5to about 50 mm, the size of each aperture 51 is preferably set to about5 mm or larger.

[0153] The function of the apertures 51 formed in the casing 56 is notto completely separate the reduced product 16 and the solid reductantfrom each other, and it is to leave a part of the solid reductant forprotection of the hearth 11. That is, the solid reductant having arelatively large grain size may be discharged together with the reducedproduct 16 to the outside of the furnace by the screw feeder 53.

[0154] When the size of each aperture 51 is set smaller than theabove-described value, the apertures 51 may be closed with grains of thesolid reductant bitten by the apertures 51. Therefore, the size of eachaperture 51 is preferably not less than about 5 mm.

[0155] Although the sidewall 54 of the casing 56 shown in FIGS. 31 and32 is provided with the apertures 51, apertures may be also formed inthe bottom plate 55 so that the solid reductant having a smaller grainsize can be easily discharged from the casing 56 onto the movable hearth11.

[0156] The apertures 51 are provided for returning the solid reductantto the movable hearth 11 through the apertures 51. Therefore, the shapeof the apertures 51 is not limited to that which is shown in FIGS. 31and 32, and it may be such that of, for example, a punched metal or anet.

[0157] The casing 56 of the discharging device 15 may be damaged fromheat and friction. Therefore, it may have a structure so that it can becooled by, for example, cooling water. The durability can be improved bybeing cooled and maintenance charges such as for renewal or repair ofthe device can be reduced.

[0158] A discharging device according to another embodiment of theinvention is described with reference to FIG. 33. The discharging deviceis provided in a discharge section of a movable-hearth furnace 10. Thedischarging device includes a screw feeder 53 which spans a movablehearth 11 and is disposed substantially perpendicular to the directionof movement of the movable hearth 11, and a reductant-dischargingshooter 61 and a reduced-product-discharging shooter 62 which aredisposed at an end of the screw feeder 53.

[0159] The screw feeder 53 includes a spiral screw 53 b about a roller.With the rotation of the spiral screw 53 b, the reduced product 16 andthe solid reductant 65 used for protecting the surface of the movablehearth 11 are transferred toward the shooters 61 and 62 and aredischarged to the outside the furnace.

[0160] The screw feeder 53 is provided with a net-basket-shapedcylindrical screen 66 which is coaxially formed at an end of the screwfeeder 53 protruding to the outside of the furnace. The rotation of thecylindrical screen 66 and the screw feeder 53 is synchronized with eachother. The reductant-discharging shooter 61 is disposed under thecylindrical screen 66, and the reduced-product-discharging shooter 62 isdisposed directly under an open end (free end) of the cylindrical screen66.

[0161] With this arrangement, the reduced product 16 and the solidreductant 65 are transferred by the screw 53 b toward the outside of thefurnace as the screw feeder 53 rotates. The solid reductant 65 which hasa smaller grain size passes the cylindrical screen 66 and is dischargedto the outside of the furnace via the reductant-discharging shooter 61.Generally, the discharged solid reductant 65 is sent to a chargingdevice such as the charging device 14 shown in FIG. 1, and is depositedon the movable hearth 11 to form the solid reductant layer 1 b forprotection of the surface of the movable hearth 11.

[0162] Accordingly, the reduced product 16 can be separated from thesolid reductant 65 while the screw feeder 53 is performing discharging.Since the solid reductant 65 can be returned onto the movable hearth 11via the charging device 14, a transfer device for a mixture of thereduced product 16 and the solid reductant 65, and screen devicesexclusive for the reduced product 16 and the solid reductant 65,respectively, are not necessary. Therefore, the overall size of thedevice can be reduced, and the configuration of the device can be madesimple. The distance of transfer of the solid reductant 65 can bereduced, whereby the temperature decrease in the solid reductant 65 canbe suppressed, thereby contributing to the reduction of energy costs.

[0163] Another embodiment according to the invention is described withreference to FIG. 34. The discharging device includes a screw feeder 53provided with a tapered part 68 toward a discharge end-part of the screwfeeder 53 on the movable hearth 11. The end part of the screw feeder 53from the tapered part 68 to the end protruding to the outside of thefurnace is formed as a reduced-diameter part 71.

[0164] The screw feeder 53 is provided with a conical collecting shooter69 which covers the screw feeder 53 coaxially with the screw feeder 53at the tapered part 68 thereof. A discharge cylinder 70 provided with anet-shaped screen 70 a about the reduced-diameter part 71 at a portionof the discharge cylinder 70 associated with the movable hearth. Therotation of the discharge cylinder 70 is preferably synchronized withthe rotation of the screw feeder 53. The reduced-product-dischargingshooter 62 is fixed to the furnace at a free end, that is, an open endof the discharge cylinder 70 protruding to the outside of the furnace.

[0165] The size of each mesh of the net-shaped screen 70 a is set sothat the reduced product 16 having a larger grain size remains in thedischarge cylinder 70 and the solid reductant 65 having a smaller grainsize falls from the discharge cylinder 70.

[0166] In the discharging device shown in FIG. 34, the reduced product16 and the solid reductant 65 are transferred by the screw 53 b alongthe movable hearth 11, are collected from the movable hearth 11 at thecollecting shooter 69, and sent into the discharge cylinder 70. Thesolid reductant 65 falls away from the discharge cylinder 70 through themesh of the net-shaped screen 70 a, and the reduced product 16 includinga metal and slag is discharged to the outside of the furnace through thereduced-product-discharging shooter 62. Since the net-shaped screen 70 aof the discharge cylinder 70 is disposed on the movable hearth 11, thesolid reductant 65 falls away from the discharge cylinder 70 through thenet-shaped screen 70 a onto the movable hearth 11.

[0167] In the discharging device according to the embodiment, the solidreductant 65 is not discharged outside of the furnace, but is left onthe movable hearth 11 to be reused, whereby handling of the solidreductant 65 outside the furnace is not necessary, and the thermalenergy can be used efficiently because the solid reductant 65 is notexposed to the outside air.

[0168] Since the collecting shooter 69 and the discharge cylinder 70 ofthe discharging device according to this embodiment are disposed in adischarge section of the movable hearth 11, it is difficult tocompletely discharge the reduced product 16 and the solid reductant 65.Therefore, a width-reducing guide plate 72 is provided, which moves thereduced product 16 and the solid reductant 65 to a side of the movablehearth 11 toward the end opposite to the discharge end of the screwfeeder 53. With this arrangement, the area of the movable hearth 11 canbe used efficiently, in which the reduced product 16 and the solidreductant 65 are moved to one side of the movable hearth 11 only in thedischarge section of the movable hearth 11.

[0169] According to the invention, as described above, damage to ahearth can be avoided, which was not possible in known dischargingoperations of a product produced on a movable hearth of a movable-hearthfurnace. The reduced product such as reduced iron can be collectedefficiently by selecting the reduced product on the movable hearth,thereby avoiding dust produced during classification performed outside afurnace, whereby the working environment can be improved. Since only thereduced product is collected and a solid reductant can be left on thehearth for reuse by being sifted, labor required for transportation andthe like for reuse of the solid reductant can be reduced. As a result,the loss of thermal energy of the solid reductant can be reduced andoperation of the furnace can be made stable.

What is claimed is:
 1. A method for discharging a reduced productproduced on a movable hearth of a movable-hearth furnace, comprising:removing the reduced product from the movable hearth; separating thereduced product from a solid reductant; either leaving substances otherthan the reduced product on the solid reductant layer or returning thesubstances onto the solid reductant layer; and discharging the reducedproduct to the outside of the movable-hearth furnace.
 2. The methodaccording to claim 1, wherein removing the reduced product from themovable hearth comprises attracting the reduced product with a magneticforce to thereby remove the reduced product from the movable hearth. 3.The method according to claim 2, further comprising: cooling the reducedproduct before attracting the reduced product.
 4. The method accordingto claim 1, wherein removing the reduced product from the movable hearthcomprises: scooping the reduced product and the solid reductant with ascreen; and separating the reduced product from the solid reductantcomprises sifting the reduced product and the solid reductant accordingto the grain size of the reduced product and the solid reductant withthe screen.
 5. The method according to claim 4, wherein sifting thereduced product and the solid reductant according to the grain size ofthe reduced product and the solid reductant with the screen such thatthe reduced product and the solid reductant having smaller grain sizesare left on the movable hearth, comprises selecting the reduced producthaving a larger grain size with a rotary drum which substantially spansthe movable hearth of the movable-hearth furnace in the widthwisedirection of the movable hearth and is provided with a plurality ofnet-shaped or comb-shaped screens each extending radially outwardly fromthe rotary drum from the periphery thereof.
 6. The method according toclaim 4, wherein sifting the reduced product and the solid reductantaccording to the grain size of the reduced product and the solidreductant with the screen such that the reduced product and the solidreductant having smaller grain sizes are left on the movable hearth,comprises removing the reduced product having a larger grain size fromthe solid reductant layer and discharging the reduced product with ascrew feeder having an axis of rotation which substantially spans themovable hearth in the widthwise direction of the movable hearth andextends outwardly of the movable-hearth furnace, and which operates insuch a manner that a part of the solid reductant is left on the solidreductant layer by controlling the position of the axis of the screwfeeder with respect to the movable hearth.
 7. The method according toclaim 6, wherein a plurality of apertures are formed in a casingsubstantially surrounding the screw feeder, the apertures being arrayedsubstantially along the axis of the screw feeder, such that the reducedproduct and the solid reductant having smaller grain sizes are left onthe solid reductant layer.
 8. The method according to claim 7, whereinthe casing provided with the plurality of apertures is a cylindricalscreen which substantially covers the screw feeder.
 9. The methodaccording to claim 6, further comprising: classifying the reducedproduct and the solid reductant according to grain size; and returningthe reduced product and the solid reductant having smaller grain sizeseither onto the solid reductant layer formed on the movable hearth ofthe movable-hearth furnace or to a layer of mixed raw materials formedon the solid reductant layer.
 10. A discharging device for discharging areduced product produced on a movable hearth of a movable-hearthfurnace, comprising: removal means for removing the reduced product fromthe movable hearth; separation means for separating the reduced productfrom a solid reductant; leaving-returning means connected to eitherleaving substances other than the reduced product on the solid reductantlayer or returning the substances onto the solid reductant layer; anddischarge means connected to discharge the reduced product outwardly ofthe movable-hearth furnace.
 11. The discharging device according toclaim 10, wherein the removal means, the separation means and thedischarge means comprise a belt conveyor which opposes the movablehearth at at least one portion of the belt conveyor and extendsoutwardly of the movable-hearth furnace, and at least one magnetprovided within a loop formed by a belt of the belt conveyor at least ata position opposing the movable hearth and adjacent to the positionoutside the movable-hearth furnace, the at least one magnet attractingthe reduced product from the movable hearth, thereby separating thereduced product from the solid reductant.
 12. The discharging deviceaccording to claim 11, wherein the at least one magnet is disposed at aposition opposing the movable hearth with the belt of the belt conveyortherebetween.
 13. The discharging device according to claim 11, whereinthe at least one magnet is fixed to a rear face of the belt of the beltconveyor.
 14. The discharging device according to claim 10, wherein theremoval means, the separation means and the discharge means comprise afirst belt conveyor which opposes the movable hearth at at least oneportion of the first belt conveyor and extends outwardly of themovable-hearth furnace, a second belt conveyor which is provided withina loop formed by a belt of the first belt conveyor and is disposed at aposition opposing the movable hearth with a lower portion of the belt ofthe first belt conveyor therebetween, rotation of the first beltconveyor and the second belt conveyor being substantially synchronizedwith each other, and having at least one magnet which is mounted on arear face of the belt of the second belt conveyor.
 15. The dischargingdevice according to one of claims 10 to 14, further comprising: ascraper disposed adjacent a portion of the belt conveyor to which amagnetic force is not applied and which is outside the movable-hearthfurnace, the scraper adapted to scrape the reduced product adhered to afront face of the belt of the belt conveyor.
 16. The discharging deviceaccording to claim 10, wherein the removal means and the separationmeans comprise a rotary drum which substantially spans the movablehearth of the movable-hearth furnace in the widthwise direction of themovable hearth and is provided with at least one magnet at least at aportion of the rotary drum opposing the movable hearth, for attractingthe reduced product disposed on the movable hearth, and the dischargemeans comprises transfer means disposed substantially parallel to theaxis of the rotary drum, and which receives the reduced productattracted to and falling from the rotary drum and transfers the reducedproduct outwardly from the movable-hearth furnace.
 17. The dischargingdevice according to claim 16, wherein the rotary drum has a rotationaldirection and comprises an outer drum and an inner roller disposedinside the outer drum and which is provided with the at least one magnetfixed to a cylindrical surface of the inner roller, said at least onemagnet extending in the rotational direction of the rotary drum from alower portion of the cylindrical surface to a portion thereof associatedwith the discharge means.
 18. The discharging device according to one ofclaims 16 and 17, wherein the discharge means comprises a belt conveyordisposed substantially parallel to the axis of the rotary drum, andwhich receives the reduced product attracted to and falling from therotary drum, and extends from the movable hearth and outwardly from themovable-hearth furnace.
 19. The discharging device according to one ofclaims 16 and 17, further comprising a plurality of protrusions on aperipheral face of the rotary drum.
 20. The discharging device accordingto one of claims 16 and 17, wherein the rotary drum is formed as acylinder having a smaller diameter at an intermediate portion in anaxial direction of the cylinder.
 21. The discharging device according toone of claims 16 and 17, further comprising a cooling member which coolsthe reduced product before the reduced product has a magnetic fieldapplied thereto to be attracted and removed from the movable hearth bythe magnetic force.
 22. The discharging device according to claim 10,wherein the removal means and the separation means comprise aclassifying member including at least one net-shaped or comb-shapedscreen protruding from a drum in a radial direction thereof, the drumsubstantially spanning the movable hearth of the movable-hearth furnacein the widthwise direction of the movable hearth, and the dischargemeans comprises a transfer conveyor which transfers the reduced productscooped from the movable hearth by the classifying member.
 23. Thedischarging device according to claim 22, wherein the transfer conveyoris disposed in the vicinity of the drum provided with the classifyingmember and substantially parallel to a rotational axis of the drum, thetransfer conveyor being disposed at a position in which the transferconveyor receives the reduced product falling from the classifyingmember.
 24. The discharging device according to claim 22, wherein thetransfer conveyor is disposed to pass through the drum in an axialdirection thereof, and the drum is provided with at least one openingformed in the drum in the vicinity of the net-shaped or comb-shapedscreen such that the reduced product scooped by the at least onenet-shaped or comb-shaped screen is received by the transfer conveyorthrough the at least one opening.
 25. The discharging device accordingto one of claims 22 to 24, further comprising: side plates individuallydisposed at sides of the movable hearth along the direction of movementof the movable hearth and adapted to prevent a deposited substance fromcollapsing.
 26. The discharging device according to claim 10, whereinthe removal means, the separation means and the discharge means comprisea screw feeder which substantially spans the movable hearth in thewidthwise direction thereof and extends outwardly from themovable-hearth furnace, and a casing disposed at a downstream side ofthe screw feeder in the direction of movement of the movable hearth, thecasing being formed with a sidewall extending along a rotational axis ofthe screw feeder and a bottom plate extending from the sidewallsubstantially parallel to the movable hearth.
 27. The discharging deviceaccording to claim 26, wherein the casing has a plurality of apertures.28. The discharging device according to claim 10, wherein the removalmeans, the separation means and the discharge means comprise a screwfeeder which substantially spans the movable hearth in the widthwisedirection thereof, a reductant-discharging shooter disposed at aposition associated with an end portion of the screw feeder protrudingoutwardly from the movable-hearth furnace, a reduced-product-dischargingshooter disposed toward an outer side of the movable-hearth furnace fromthe reductant-discharging shooter, and a cylindrical screen which coversthe end portion of the screw feeder associated with the position atwhich the reductant-discharging shooter is disposed, rotation of thecylindrical screen being substantially synchronized with that of thescrew feeder; and wherein the reduced-product-discharging shooter ispositioned at an open end of the cylindrical screen.
 29. The dischargingdevice according to claim 10, wherein the removal means, the separationmeans and the discharge means comprise a guide plate disposed in adischarge section of the movable hearth, for reducing the width of anaccumulative layer of the reduced product and the solid reductant, and ascrew feeder disposed in a direction substantially perpendicular to thedirection of movement of the movable hearth and provided with a taperedportion toward a discharge end of the screw feeder on the movablehearth, an end portion of the screw feeder from the tapered portion tothe end thereof protruding outwardly from the movable-hearth furnacebeing formed as a reduced-diameter part; and wherein a conicalcollecting shooter is disposed at the tapered portion of the screwfeeder, a discharge cylinder is disposed about the reduced-diameterportion of the screw feeder toward the discharge end thereof from theconical collecting shooter, the discharge cylinder being provided with anet-shaped screen at a portion of the discharge cylinder associated withthe movable hearth, and a reduced-product-discharging shooter isprovided at an open end of the discharge cylinder disposed outwardlyfrom the movable-hearth furnace.